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On the one hand moving to display seems >>>>> appropriate, but adding any new stuff to xe_display.c means more stuff >>>>> to clean up for later. >>>>> >>>>> As you know, i915 does this as well in i915 core. The next logical step >>>>> is then to have this in i915/display, and share the code between i915 >>>>> and xe. Adding another interface for i915/display. >>>> humn... but what would be the alternative? Move the i915 one to >>>> i915/display and then make both xe-core and i915-core use that? >>>> If we move it to display/ here then we can land this and finish the >>>> cleanup later. >>> The alternative would be to keep it outside of display/ in both drivers, >>> because display doesn't appear to need it. The annoying part in that is, >>> obviously, that display should take care of display stuff. >> This whole code seems rather dodgy. I see Windows has similar code >> so I presume that's where it came from. But does anyone know what >> this "Broadwell divider mode" actually does? > +Lionel, since you wrote the original code for this in commit > dab91783338b ("drm/i915: expose command stream timestamp frequency to > userspace") do you happen to remember if there was any other > documentation on the CTC_MODE setting? I.e., what "Broadwell divider > mode" (the description in the bspec) actually means and how we should > know to use a display reference clock in that case? I don't remember this stuff having anything to do with display HW (is TIMESTAMP_OVERRIDE part of the display HW?). And yes, I had to read the windows code to get what register to read based on the value of CTC_MODE because there is no documentation about that afaict. -Lionel > > > Matt > >> If we assume that it means the display refclk is also used to >> generate the CS timestamps (I'm really suprised to learn that >> maybe there are systems with different refclks for display vs. >> GT) and that TIMESTAMP_CTR is always generated from the display >> refclk then display already reads that out from >> DSSM, no need to read out the TIMESTAMP_OVERRIDE. >> >> Also the current code that reads TIMESTAMP_OVERRIDE doesn't >> even seem to check whether the override is actually enabled. >> IIRC I saw bit 30==enable at least on some platforms... That bit seems deprecated since 396385 398004 (Gfx9 era) >> >> -- >> Ville Syrjälä >> Intel